The clinical diagnosis of antiphospholipid syndrome (APS) requires the detection of the persistent presence of circulating antiphospholipid antibodies (aPL) in association with clinical symptoms such as vascular thrombosis and recurrent pregnancy losses. The laboratory criteria of aPL for the classification of APS include lupus anticoagulant (LA), anticardiolipin antibodies (aCL), and anti-β2-glycoprotein I antibodies (anti-β2GPI) (refs. 1-3; herein incorporated by reference in their entireties). However, in some instances, patients with clinical manifestations highly suggestive of APS lack any of the previously mentioned aPL (refs. 4-8; herein incorporated by reference in their entireties). These are referred to as seronegative APS. Accumulating evidence has shown that antibodies directed against phosphatidylethanolamine (PE) lipids, a class of lipids with zwitterionic PE head group, are strongly associated with similar or identical clinical symptoms of APS, in the absence of the laboratory criteria of this syndrome (refs. 9-11; herein incorporated by reference in their entireties). The investigation of anti-PE antibodies (aPEs) would impact the clinic diagnosis of unexplained thrombosis and recurrent pregnancy losses, therefore benefits the treatment outcome of APS.
ELISA is the most common assay for the detection of aPE in patient serum samples. However, there is currently no standardized aPE ELISA protocol, and a number of variations in aPE ELISA conditions have been reported in aPE literature. It has been shown that different sources of PE impact ELISA signals to some extent. Other variations in ELISA assay are attributed to the material of microplates, buffer systems and cofactor supplement used for aPE detection (refs. 12-15; herein incorporated by reference in their entireties). Altogether, prior studies reveal an inconsistent comparison among aPE detection data from different laboratories and raised a need for standardization of the assay.